PET-CT emerged as a new diagnose modality with relatively low false negative rate.Our study aimed at exploring the clinical factors that identified false negative N2 in PET-CT.
From January 2008 to June 2013, 802 NSCLC patients underwent PET-CT scan followed by curative intent resection. The following patients were excluded: patients who received neo-adjuvant chemotherapy or radiotherapy, those diagnosed as central lung tumor, patients with PET-CT diagnosed lymph node involvement (N1-N3). Lymph node was diagnosed negative when short axis less than 1cm and SUVmax less than 2.5. 284 patients were reviewed and none received invasive mediastinal staging. Clinicopathological data were retrospectively analysed to identify their asscociation with occult N2 metastasis. We collected 156 patients treated from July 2013 to December 2014 as test set to validate the former results.
8.5% (24/284) PET-CT diagnosed N0 NSCLC had pathological proved N2 metastases. The SUVmax of primary tumor is the sole independent risk factor of occult N2 NSCLC (P = 0.003, 95% CI:0.81-0.96, OR = 0.88). Occult N2 metastasis occurred more frequently in 7# (16/24) and 4R# lymph node(12/24). Accordingly, we divided our patients into two groups: 1. SUVmax < 2.6 with an occult N2 incidence rate of 1.0% (1/100); 2. SUVmax ≥ 2.6, with a rate of 12.5% (23/184). In the test set, the occult N2 incidence rate was 9.6% (15/156). The 7# (9/15) and 4R# lymph node(7/15) were the station with higher occult N2 incidence rate, and in two groups, the occult N2 rate was 3.8%(2/52) and 12.5%(13/104), respectively.
SUVmax of primary tumor is independent risk factor of occult N2 metastasis in PET-CT diagnosed N0 disease. SUVmax ≥ 2.6 of primary tumor should be investigated further with invasive mediastinal staging modality or systematic lymph node dissection be performed, and subcarinal lymph node and low paratrachea lymph node should be biopsied or removed. Invasive mediastinal staging can be spared in patients with SUVmax < 2.6 and proceed directly to curative intent surgery, especially when GGO component was detected. In decision-making of performing invasive mediastinal staging, SUVmax should be taken into account as an evaluation indicator.
Clinical trial identification
All authors have declared no conflicts of interest.